Cracking and recovery of hydrocarbons

ABSTRACT

THIS APPLICATION DISCLOSES METHODS AND APPARATUS FOR CRACKING HYDROCARBON FEEDSTOCKS, IN WHICH A SOLID CARBONACEOUS FUEL IS BURNED WITHIN A CRACKING ZONE TO SUPPLY THE TEMPERATURE AND THE HEAT REQUIRED FOR THE ENDOTHERMIC CRACKING REACTION. A REACTOR IS ALSO DISCLOSED WHICH HAS IN IT AN EDUCTOR TUBE THAT IS OF REDUCED CROSS-SECTIONAL AREA WITH RESPECT TO THE CRACKING CHAMBER FOR PREFERENTIALLY RECOVERING FROM THE INTERIOR OF THE REACTOR   A STREAM RICH IN CRACKED PRODUCTS AND LEAN IN COMBUSTION PRODUCTS AND ASH.

Feb. 23, 1971 Filed July 31, 1967 FIG. L

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INVENTOR H. N. HICKS, JR

CRACKING AND RECOVERY OF HYDROCARBONS 4 Sheets-Sheet 1 Harold N. Hicks,Jr.

ATTORNEY Feb. 23, 197-1 H. N. HICKS, JR- 3,565,968 I CRACKING ANDRECOVERY OF HYDROCARBONS Filed July 51, 1967 4 Shee ts-Sheet 2 FIG. 2.

FIG. 3.

26 FIG.4. H7

) J INVENTOR 85 v 4 Harold N. Hicks, Jr.

ATTORNEY Feb. '23, 1971 H. N. HICKS, JR 3,

CRACKING-AND RECOVERY OF HYDROCARBONS Filed July 51, 1967 '4Sheets-Sheet FIG. 5A.

W 43 7 Z/ 5 Q) l//// INVENTOR Harold N. Hicks,Jr.

ATTORNEY Feb. 23, 1971 H. N. HICKS. JR

CRACKING AND RECOVERY OF HYDRQCARBONS Filed Jul 51, 19s? FIG. 5B.'

4 Sheets-Sheet 6 INVENTOR Harold N. Hicks, Jr.

BY ifZ YWJIA.

ATTORNEY United States Patent 3,565,968 CRACKING AND RECOVERY OFHYDROCARBONS Harold N. Hicks, Jr., Huntington, W. Va., assignor toAshland Oil & Refining Company, Houston, Tex., a corporation of KentuckyFiled July 31, 1967, Ser. No. 657,342 Int. Cl. C07c 3/30 US. Cl. 26068337 Claims ABSTRACT OF THE DISCLOSURE This application discloses methodsand apparatus for cracking hydrocarbon feedstocks, in which a solidcarbonaceous fuel is burned within a cracking zone to supply thetemperature and the heat required for the endothermic cracking reaction.A reactor is also disclosed which has in it an eductor tube that is ofreduced cross-sectional area with respect to the cracking chamber forpreferentially recovering from the interior of the reactor a stream richin cracked products and lean in combustion products and ash.

BACKGROUND OF THE INVENTION The broad field of the invention is thecracking of hydrocarbons. Mor particularly the invention relates to theproduction of unsaturated hydrocarbon products by cracking hydrocarbonfeedstocks having a higher degree of saturation than the unsaturatedhydrocarbon products produced therefrom. In one specific aspect, theinvention pertains to the production of acetylene and ethylene mixtures.

Despite the fact that the patent art and literature are replete with awide variety of different processes and apparatus for carrying out thecracking (pyrolysis) of hydrocarbon feedstocks (e.g., to acetylene and/or ethylene), only a relatively few of the suggested processes andapparatus have achieved significant commercial status. Among the varioustypes of processes which have attained some degree of commercialimportance are: are processes, in which the hydrocarbon feedstock isheated to its pyrolysis or cracking temperature by passing an electricdischarge therethrough; the Wulff Process, in which a regenerativereactor comprising a heat absorptiondesorption mass (e.g., refractorybrick checkerwork) is alternately (a) heated by hot combustion gases and(b) used to heat feedstock to its cracking temperature by direct heatexchange; and partial combustion processes in which feedstock is fed toa reactor along with only enough oxygen to burn part of the feedstock,and the resultant heat is used to convert the remainder of the feedstockto cracked products.

In addition to the types of processes just described, the prior artsuggests many other processes and apparatus which, though theoreticallyoperable, nevertheless suffer from various practical disadvantages whichrender them either uneconomical or exceedingly difficult to control andoperate consistently. Among the various considerations which havediscouraged the commercial utilization of such other known processes arehigh general opera tion and maintenance costs which are peculiar to thevarious processes, high energy costs and high feedstock costs. Some ofthese same disadvantages also apply to those processes which have comeinto commercial use.

Factors which contribute to the general operating and maintenance costsof a given process include: the rate of throughput which is feasible forthe process and its associated equipment, the concentration of thedesired products, and the type and concentration of undesired products,which factors determine the amount of investment Patented Feb. 23, 1971needed for a plant of given production capacity; any special proceduresinvolving the exercise of unusually close operating control, which mayresult in high labor costs and occasional malfunctions; and anyrequirements for circulating materials other than feed and fuel throughthe process, thus necessitating the provision of apparatus forintroducing and/ or removing such additional materials. Thelast-mentioned factor will be discussed in further detail hereinafter.

As indicated previously, high energy costs are an undesirable feature ofsome of the known processes. Energy cost refers to the actual cost ofenergy in the production of a unit weight or volume of product. Suchfactors as the type of energy source employed and the thermal efficiencyof the process and apparatus enter into the overall energy costs. Forinstance, in a process in which the heat is supplied in the form ofelectrical energy which heats the feed directly, e.g. by electricaldischarge, or indirectly, e.g., by heating resistance coils whichcontact the outer surface of the cracking chamber, energy costs will bequite high. The electricity used in such process may, for instance, beobtained from an electrical generating plant which burns coal, and theelectrical power generating plant may recover only about 40% of the heatenergy available from the coal. In certain other processes, thermalefiiciency is a critical factor. For instance, in some of theprecombustion processes which have been suggested, in which a hotgaseous medium is formed by combustion in one chamber and is thentransferred to another chamber where it is mixed with the cracking stockto heat the stock to cracking temperature by direct heat exchangetherewith, heat losses due to conduction, radiation, etc. tend to berather substantial, thus resulting in a lower thermal efliciency andrequiring the utilization of more fuel per unit product produced, withconsequent greater expense than would otherwise be necessary.

As suggested above, high feedstock costs detract from the attractivenessof some of the known processes. In this connection, it should beunderstood that where a given process requires a special type offeedstock which is more expensive than the feedstocks generally employedin other cracking processes, the process in question will be at aneconomic disadvantage in this respect. Feed costs are also affected byyield considerations. Yield, the percentage of the feedstock which isactually converted to the desired product in recoverable form ascompared to the amount that is theoretically convertible, will beadversely affected where the process in question tends to encouragecompeting reactions (e.g., combustion of the feed, water gas reactionand so forth) or where the process or apparatus is incapable ofsubjecting the feedstock to the correct time/temperature history. Theconcept of time/temperature history, its importance, and certaincomplicating factors involved in attaining same will now be discussed byreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings which accompany thisspecification, in which uniform reference numerals are employed toidentify the same parts when they appear in more than one view, and inwhich the various parts are not to scale:

FIG. 1 is a schematic diagram of a precombustion type pyrolysis reactorlinked with a graph illustrating the hypothetical temperature andresidence time of the flow of a selected feedstock and products whichmight pass through such apparatus;

FIG. 2 is the first of seven figures disclosing a portion of a thermalcracking apparatus constituting a preferred embodiment of the apparatusof the present invention, FIG. 2 being a sectional view which shows asolid fuel storage and feeding device for such system;

FIG. 3 is a partially broken-out sectional view showing a solids ejectorwhich connects to the bottom of the feeding device of FIG. 2.

FIG. 4 is a diagram of the solids feeding system, including the feedingdevice and ejector of FIGS. 2 and 3, a grinder and associated piping;

FIG. 5A is a sectional view of the upper portion of a burner andcracking chamber assembly which connects with the solid feedingapparatus shown in FIG. 4;

FIG. 5B is a sectional view of the lower portion of the cracking chambershown in FIG. 5A and the product collection chamber which connectstherewith;

FIG. 6 is a sectional view of the burner assembly of FIG. 5A, takenalong section line 6-6; and

FIG. 7 is a diagram of a collection system which is connected to theeductor tube of the cracking chamber shown in FIG. 5B.

Time/ temperature history discussion The concept of time/temperaturehistory is applicable to virtually any process for the cracking ofhydrocarbons. However, for puropses of simplified explanation, it willbe discussed in connection with a prior art precombustion process forproducing acetylene and ethylene. Precombustion processes differsomewhat from partial combustion processes. In the latter, part of thefeedstock is burned in the same chamber in which cracking takes place.In the usual precombustion process, combustion and crack ing take placein separate chambers, so that the feedstock which is to be cracked doesnot come under the influence of the flames from the combustion.

In the precombustion type reactor shown in FIG. 1, which has beengreatly simplified for purposes of illustration, the reactor comprises atubular chamber 1 having an inlet end 2 and an outlet end 3. Downstreama short distance from inlet end 2 are a plurality of identical feedstockinlets 4, which communicate with the interior of chamber 1. A shortdistance upstream from outlet end 3 is a quench nozzle 5 and supplypipe, which also communicate with the interior of chamber 1.

The flows of materials into, through and out of the above-describedreactor are represented by a number of arrows. Arrow 6 represents a flowof hot gaseous heating medium (e.g. inert combustion gases at atemperature of say 4000" F.) which enter inlet end 2. The gaseousheating medium is prepared in a combustion chamber (not shown) which isentirely separate from chamber 1, but which communicates therewiththrough inlet 2. Arrows 7 represent gaseous hydrocarbon feedstock (e.g.propane, preheated to 900 F.) which enters through inlet 4 and promptlymixes with and is heated by the gaseous heating medium 6. The feedstockis preheated in a preheater (not shown) which is also separate fromcracking chamber 1. As the reaction mass 11 (the resultant hot mixtureof gaseous heating medium 6 and feedstock 4) forms, the continuousintroduction of additional gaseous heating medium and feedstock pushesthe reaction mass downstream in chamber 1 towards the quench nozzle 5,and the heated feedstock therein cracks to acetylene and ethylene. Uponarrival at the quench nozzle the reaction mass 11 promptly mixes with aflow of relatively cool quench fluid (e.g. water, hydrocarbon, or othersuitable coolant), represented by arrows 8, and is cooled thereby to atemperature so low that cracking is substantially completely terminated.The mixture of quench fluid, reaction products and by-products,represented by arrow 9, departs the reactor through outlet end 3.

FIG. 1 includes a graph in which the horizontal axis is a time axis,positioned so that its left end lies directly below the feedstock inlets4, and its right end lies directly below outlet end 3 of crackingchamber 1. The time axis is marked off in thousandths of seconds(seconds X 10- the left end of the time axis being arbitrarily labeled 0seconds to represent the instant when a selected portion of the reactionmass begins its journey from the vicinity of the feedstock inlets to thevicinity of the quench nozzle 5. A reference line 10 extends from thecenterline of quench nozzle 5 to the time axis of the graph to show thattime during the travel of the reaction mass when it is cooled by thequench fluid. The vertical axis of the graph is marked off in degreesFahrenheit to show the temperature prevailing within the selectedportion of reaction mass at different times as it journeys through thechamber. Under steady state conditions (e.g., when the flow rates, thecomposition and the injection temperatures of the feedstock, the gaseousheating medium, and the quench fluid and the temperature of thesurroundings are all holding constant) every cubic inch of the reactionmass which forms near inlets 4 and travels along the axis of chamber 1past quench nozzle 5 will heat up and cool off on the same time scheduleas succeeding cubic centimeters of the reaction mass. The relationshipwhich exists between the temperatures of the feedstock, reaction massand products at various stages of the reaction and the sequence and timeintervals in which the materials are subjected to such temperatures isreferred to as the time/ temperature history of the process, whichhistory is most conveniently represented in graphical form, asillustrated in FIG. 1.

The importance of subjecting the hydrocarbon feedstock to a proper time/temperature history results from the fact that within the broad range oftemperatures which will induce some pyrolysis of hydrocarbons there arecertain temperatures which favor the production of acetylene, stillother temperatures (generally lower) which favor the production ofethylene, and still other temperatures (both higher and lower) whichfavor the production of still other products such as di-acetylene,carbon black, and tar, which may or may not be desired. Thus, there isan optimum cracking temperature to which one must subject the feedstockin order to recover a particular desired product or product mixture.Generally speaking, the invention yields particular advantages in theproduction of mixtures of acetylene and ethylene, and the relativeratios of acetylene and ethylene in the product mixture may beinfluenced somewhat by the temperature to which the feedstock, as wellas the resultant products, are subjected. To the extent that the optimumoperating temperature corresponding to a particular desired mixture ofproducts is not uniformly maintained during the cracking reaction,varying quantities of unwanted products will be produced, thusdowngrading some feedstock. Also, as will be appreciated by thoseskilled in the art, the subjection of the feed to a proper time/temperature history is an essential factor in achieving high percentagesof conversion of the feed in a single pass, e.g. without recycling.Accordingly, in order to obtain the desired product mixture, attemptsshould be made: (a) to reduce insofar as possible the period of timerequired to heat the feed to the optimum temperature; (b) to maintainthe temperature of the reactants as nearly constant as possible at theopimum temperature while the cracking reaction is taking place; and (c)to reduce insofar as possible the length of time required to cool thereaction mixture upon completion of the reaction. To the extent thatthese objectives are realized, the total period of time during which thefeed hydrocarbon will be subjected to temperatures which produceunwanted products will be curtailed, and a proper time/temperaturehistory will thereby be attained, leading to the desired mixture ofproducts (e.g. acetylene-ethylene) in the product stream.

A hypothetical idealized time/temperature history for production of anacetylene-ethylene mixture rich in acetylene may be illustrated byreference to the dashed line 12 in the graph of FIG. 1. Line 12 has itsorigin of a time of 0 and a temperature of slightly less than 1200 F.,which represents a desirable upper limit for the preheating of somecracking stocks. The hypothetical reaction mass and a selectedhypothetical feedstock are heated instantaneously to the desiredcracking temperature, e.g. 3150 F. Thus, without being subjected tointermediate temperatures for any appreciable time, the feedstocktemperature goes from below 1200 F. to 3150 F. The temperature of thefeed is then held at precisely 3150 F. until 2.5 thousandths (2.5seconds have passed, at the end of which time the temperature of thereaction mass and included products are instantaneously lowered to about800 F., a temperature at which further reaction of the products is notto be expected.

The time/temperature history depicted by dashed line 12, thoughdesirable, is unrealistic for a number of reasons. First of all, nomethod is known of either instantaneously heating or cooling thereaction mass. Thus, the step of heating and cooling the reaction massmust occupy an appreciable time period, during which periods the feedand at least some of the products are at temperatures other than theoptimum cracking temperature, thus encouraging undesired reactions andreducing yield. Secondly, hydrocarbon cracking processes of the typedescribed are highly endothermic on nature. That is, each molecule offeedstock which cracks in the reaction zone absorbs an amount of heatenergy from the reaction mass. The heat energy absorbed by all thecracking molecules, considered in the aggregate, constitutes asubstantial withdrawal of heat from the reaction mass during thereaction. Applying this fact to the usual precombustion process, inwhich the feedstock is heated solely by admixing it at the beginning ofthe reaction with precombusted gases, it will be apparent that as anyselected portion of the reaction mass moves downstream from the point ofmixing and as the reaction continues, the temperature of the reactionmass will drop as molecules of feedstock are cracked. If the chargingtemperatures and flow rates of the gaseous heating medium and feedstockare adjusted to impart the optimum cracking temperature to the re actionmass at the beginning of the reaction period, the temperaure will fallto well below optimum towards the end of the reaction period, thusencouraging undesired side reactions and reduced yield during thatinterval. The foregoing statement assumes that the reactor is operatedat high (economically realistic) feedstock to oxidant plus fuel ratios,which is of course a desirable condition. A third reason is that thetemperature of the reaction mass will tend to fall during the reactionfor other reasons. There are inevitable losses of heat to the atmospherefrom any production size cracking unit, and such losses of heat cool thereaction mass, lowering its temperature as it progresses through thereactor. Thus, in order to keep the average temperature of the reactionmass at the optimum level in a precombustion reactor of the typediscussed above, it is necessary to adjust the charging temperatures andflow rates of the gaseous heating medium and feedstock so that thereaction mass will initially attain a temperature significantly aboveoptimum and, towards the end of the reaction period, will fall to atemperature well below optimum, as suggested by solid line 13 in thegraph. This, however, as plainly shown in the graph, results insubjecting the feed and products to temperatures significantly above andbelow the optimum cracking temperature during a substantial portion oftheir period of reaction, thus encouraging unwanted side reactions anddiminishing both the yield and thermal efficiency of the process.

Certain known processes suggest partial solutions to certain of theabove problems. For instance, it has been proposed that the temperaturewithin the reaction zone of a precombustion or partial combustion typecracking apparatus be stabilized by diluting the reaction mass withsteam. However, temperature stabilization is achieved in this manner atthe expense of thermal efiiciency and yield of high value products.

It ha also been proposed to stabilize the temperature within thereaction zone of a precombustion type cracking reactor by vaporizingcertain temperature-stabilizing substances in the combustion zone sothat they become part of the reaction mass and travel through thereaction zone along with the hot combustion gases and feedstock. Variousmetal oxides and salts have been proposed as temperature stabilizingsubstances. The vaporization of these substances extracts heat from thehot combustion gases in the combustion zone and stores such heat aslatent heat of vaporization. When the feedstock is subsequently added tothe mixture of hot combustion gases and vaporized metallic salt oroxide, the endothermic reaction abstracts energy from the flameproduct-vapor mixture and the vapors condense, yielding the storedlatent heat as sensible heat to replace the abstracted heat and thusstabilizing the temperature within the reaction zone. While such processdoes assist in the maintenance of stable temperature conditions withinthe reaction zone, it also requires the circulation of an extraneousmaterial (a material other than fuel and feedstock) through the system,requiring additional equipment such as heaters, reservoirs, circulatingpumps and devices for the temperature stabilizing additives.

Still another proposal for stabilizing temperatures within the reactionzone of a cracking reactor is to provide an electrical heating elementextending longitudinally through the cracking chamber from one endthereof to the other. The electrical heating element adds heat to thereaction mass throughout the length of the reaction zone, thus tendingto make up for the heat abstracted by the endothermic cracking reactionand thereby exerting a stabilizing tendency upon the temperature of thereaction mass. However, in such reactors, heat is transferred to thefeedstock through a wall of the cracking chamber, and the heat transferrates of acceptable refractory materials are so slow as to inevitablyproduce an undesirably poor time-temperature history in production sizeequip ment. Accordingly, this proposal, though of considerableexperimental and theoretical interest from the standpoint ofdemonstrating the high yields of product that can be obtained underreasonably stable reaction temperature condition, suffers from thedisadvantage of becoming inefiicient when scaled up. Accordingly, it isevident that the art would be benefited by the development of a crackingprocess which i capable of subjecting a feedstock and the resultantproducts to a near ideal time/temperature history Without the losses inthermal efficiency, the complications and costs of circulatingextraneous materials through the reactor and the high energy cost whichare experienced with the steam dilution, circulation of volatile saltsand retains the foregoing advantages even when scaled up for commercialoperations.

There is a definite need for improvements in the efficiency of processesand apparatus for cracking hydrocarbons to acetylene and mixtures ofacetylene with ethyl ene, since the growth rate for industrialutilization of ethylene is currently higher than that of acetylene, thistrend being due in no small part to the fact that certain chemicalsformerly based on acetylene are now being made from ethylene in view ofsignificant reductions which have been realized in the cost ofproduction of the latter material. It is believed, therefore, that thereis a need for improvements in the efficiency of producing acetylene ifacetylene is to maintain or improve it position as a raw material.

OBJECTS It is an object of the present invention to fulfill theabove-mentioned need. Another object is to provide an apparatus andprocess for subjecting a hydrocarbon cracking stock to a time/temperature history which discourages yield losscs from unwanted sidereactions. Yet another object is to provide processes and apparatus forcracking hydrocarbons to acetylene-ethylene mixtures at a low energycost per pound of product. Still another object is to provide processesand apparatu for cracking hydrocarbons in which the thermal energyrequired for the endothermic cracking reaction is transferred to thereaction mass in an extremely rapid manner. Another object is to providea cracking process in Which the cracking stock is heated to a verysubstantial extent by high emissivity, incandescent particles ofcarbonaceous fuel. Yet another object is to provide processes andapparatus for conducting a cracking reaction with a very high level ofthermal efliciency. Still another object of the invention is to provideprocesses and apparatus for conducting a cracking reaction to producethe desired cracked products at high levels of concentration, thusfacilitating their recovery. Yet another object of the invention is toprovide processes and apparatus for conducting a cracking reaction whileminimizing formation and adherence of undesired deposits in the crackingapparatus. Another object is to provide a cracking process employing asolid carbonaceous fuel as the heat source and in which the fuel isburned in the same chamber in which the cracking reaction takes place,but in which the feedstock and burning fuel are maintained substantiallyseparate from one another. These and other objects of the invention willbecome apparent to those skilled in the art upon consideration of thefollowing description of the invention and certain preferred embodimentsthereof.

SUMMARY STATEMENT ON THE FEATURES OF THE INVENTION The foregoing objectsare attained in a process which includes a combination of features. Somefeatures, constituting a part of the overall process described below,may be used separately from the other features. Nevertheless, theobjects of the invention are most readily obtained when all of thefeatures are used in combination. In accordance with the overall processdescribed herein, a gaseous hydrocarbon cracking stock, a particulatecarbonaceous fuel and a gaseous oxidant are continuously fed into andare caused to flow rapidly through a confined cracking zone. In thezone, the carbonaceous fuel is burned in the presence of, but for themost part separate from, the hydrocarbon feedto provide the heatnecessary for cracking the latter to cracked products. The feedstock isfed into the cracking zone in the form of one or more streams separatefrom the carbonaceous fuel and the oxidant. The solid fuel and the majorportion of the oxidant are preferably kept separate from one anotheruntil they enter the cracking zone, and the carbonaceous fuel isintroduced in a substantially intervening relationship between thefeedstock and the oxidant, thus discourging combustion of the feedstock.The rate of combustion is controlled as necessary, by adjustment ofparticle size, air preheat temperature, fuel/ oxidant ratio andintensity of mixing of fuel and oxidant, for sustaining the combustionof said particles substantially throughout the length of the crackingzone. Preferably, combustion of said particles is completedsubstantially at the downstream end of said cracking zone or at leastprior their departure from the reactor. Thus, the hot, high emissivity,incandescent, burning carbonaceous fuel particles radiate heat into thefeedstock substantially throughout the entire length of the crackingzone, thus continually adding heat to the reaction mass to make up forheat abstracted by the endothermic cracking reaction. If the fuel issubstantially completely burned to ash and hot combustion gases onreaching the downstream end of the cracking zone, the necessity ofrecovery and rehandling of fuel solids is eliminated. As a consequenceof the relatively low hydrogen content of the solid carbonaceous (asopposed to most liquid hydrocarbon) fuel, the by-product gases are lowin water vapor content. Thus, the vapor pressure of water in thereaction zone is substantially reduced, with consequent reduction ofloss of product through the water gas re action.

As indicated above, the carbonaceous fuel is burned substantiallyseparate from the hydrocarbon feed in the same chamber in aside-by-side, adjacent relationship. The terminology substantiallyseparate is intended to indicate that throughout its exposure to theburning fuel,

the feedstock is kept sutficiently out of contact with the fuel andoxidant to prevent combustion of a major portion of the feedstock. It isnot necessary to trace the exact flow paths, concentration gradients orlines of demarcation between the streams of feedstock and burning fuelto determine whether this condition has been met, in view of the factthat hydrocarbons generally combust much more readily than solidcarbonaceous fuel. Accordingly, any hydrocarbon fuel which is subjectedto sufficient contact with burning fuel and oxidant to ignite same willcompete vigorously with the carbonaceous fuel for any available oxygenand the question of whether the major portion of the feedstock is beingkept sufliciently separate from the fuel and oxidant may be determinedfrom analysis of the combustion and cracking products by proceduresknown to those skilled in the cracking art.

In accordance with certain apparatus aspects of the invention, animproved cracking reactor of the type having fuel, feedstock and oxidantintroduction means, a cracking chamber and quenching means, is provided.The cracking chamber of such a reactor is defined by upstream anddownstream ends connected by side wall means. The transverse spacing ofthe wall means may vary from point to point along the length of thereactor, but the side wall means should be free, at least in thatportion of the cracking chamber upstream of the quenching means, fromabrupt changes in cross-section, from choke-like restrictions and fromwall roughness and projections of a character which would bring aboutthorough turbulent mixing of the feedstock and fuel flowing through thechamber. The length of the cracking chamber may be equal to or lessthan, but is preferably greater than, its width. The feedstockintroducing means is (are) connected with the interior of the chamberthrough a nozzle means situated at the upstream end of the chamber. Thenozzle means include(s) a stream-forming member for forming thefeedstock into a stream and projecting it through the chamber along aflow path which extends downstream in the chamber and is spaced inwardlyfrom the side wall means thereof.

In accordance with the improvements provided by the present invention,the aforesaid type of reactor is equipped with a stream-forming memberformed and disposed for confining at least the major portion of thefeedstock stream to a flow path which occupies less than about half ofthe transverse cross-sectional area of the cracking chamber along thatportion of its length which is upstream of the quench means. Preferably,the stream forming member is a substantially straight run of tubularconduit having a generally circular cross-section and a length todiameter ratio of at least about twenty to one, which terminates in anunrestricted opening at the upstream end of the cracking chamber, saidopening being spaced inwardly from the side wall means of the chamber onall sides. Surrounding the feedstock inlet at least in part (andpreferably substantially completely) and spaced outwardly therefrom inthe first end is (are) means for introducing at a controlled rate acontinuous flow of solid carbonaceous fuel into the cracking chamberwith components of motion downstream in said chamber and divergent fromthe general direction of movement of the feedstock stream. Surroundingthe fuel inlet means at least in part (and preferably substantiallycompletely) and spaced outwardly from the fuel introducing means is(are) oxidant introducing means for producing an envelope of oxidantsurrounding the fuel and for directing the oxidant downstream whilekeeping it spaced outwardly from at least the major portion of thefeedstock stream. Any known means for quenching and recovering thecracked products may be connected with the downstream end of thecracking chamber, but it is preferred to employ the eductor disclosedherein.

The combination of the stream-forming means which confines the feedstockstream as above described and the solid fuel introducing means whichimparts to the fuel a component of motion divergent from the directionof the feedstock stream coacts to maintain the feedstock stream andburing fuel substantially separate from one another along that portionof the length of the cracking chamber upstream of the quenching means.That fact that the fuel solids introducing means at least partlysurrounds the feedstock introducing means and is between the feedstockand oxidant introducing means tends to shield the feedstock stream fromthe oxidant and further tends to bring about consumption of most of theoxygen before much inter-diffusion of the feed and oxidant can takeplace. While in actual practice the feedstock stream on the one hand andthe burning fuel and oxidant on the other may not actually continuethroughout the entire length of the cracking chamber as substantiallycompletely discrete and physically separated streams, it should beapparent that if all but a small portion, i.e. less than about 20% ofeach stream is prevented from diffusing into the other, as a result ofthe above-described features of the reactor, the requirement of keepingthe streams substantially separate will be amply fulfilled. The extentof interdiifusion between the streams may be determined by calculationfrom an off-gas and cracked products analysis using formulae andassumptions familiar to persons skilled in the analysis techniquesemployed in the cracking art, or may be determined by the use ofradioactive tracer elements.

The eductor, which comprises another apparatus aspect of the presentinvention, is a product withdrawal arrangement. It is applicable to anycracking reactor which, in the course of its operation, has availablesubstantially separate streams of cracked products and combustionproducts in different but adjacent portions of the same chamber, and isparticularly effective in that category of reactor which produces astream of combustion products which at least partly surrounds asubstantially separate stream of cracked products. The reactor discussedabove falls in this category. The eductor is a tube of restrictedcross-section which is placed in the reactor so as to have one or moreinlet parts in the cracking chamber at a chosen point or points wherethe concentration of cracked products is higher than the concentrationof combustion products. Preferably the chosen point is that point wherethe cracked products are present at substantially the highestconcentration available in the cracking chamber when the reactor is inoperation. In a furnace having a circular cylindrical cracking chamberwith an axial feedstock nozzle surrounded by annular fuel and oxidantinjection means located at its upstream end, the eductor tube ispreferably mounted on the longitudinal axis of the chamber, downstreamof the feedstock nozzle with its inlet r port directed toward thefeedstock nozzle to permit direct entry of the cracked products withoutchange of direction. The port and tube are preferably of lessercross-sectional area than the portion of the cracking chamber in whichthey are located. The minimum distance between the feedstock nozzle andthe eductor tube inlet port is determined by the rate at which thefeedstock and resultant cracked products flow through the chamber andthe residence time needed to complete the cracking reaction. The maximumdistance is determined by the distance over which the feedstock-productstream and the fuel/oxidant-combustion product streams may flow inside-by-side relationship and remain substantially separate. Adjacentthe inlet port, in the cracking chamber, and preferably surrounding theport at least in part, is (are) passage means constituting a flow pathdiscrete from that through which the products are withdrawn, forconducting combustion products away from the port. In the tube,preferably closely adjacent the port, are means for introducing quenchfluid into the products which depart through the tube. Preferably, meansare provided for circulating coolant, which may be quench fluid, withinthe walls of the tube. The eductor tube is connected with means forproducing a controlled negative pressure differential between theinterior of the reaction zone proper and the interior of said 10 tube,whereby the cracked products may be recovered in said tube in preferenceto combustion products and ash.

CONSIDERATIONS RELATING TO MATERIALS, OPERATING DATA AND PRODUCTS Ingeneral, the invention may be carried out with any and all fluidicaliphatic and alicyclic hydrocarbons. Fluidic refers to hydrocarbonswhich may be gaseous, vaprous, liquid or even solid or semi-solid atambient temperatures, but which are capable, either in their naturalstate or after suitable pretreatment known to persons skilled in thecracking art (e.g. heating, atomization, dilution, and so forth), ofbeing readily pumped, transferred through conduits and fed to theprocess as above described, in a fluid condition. It is preferred,however, to use hydrocarbons which may be introduced into the crackingchamber in a gaseous (includes both true gases and vapors) state. Thus,the term hydrocarbon, sometimes referred to as more saturatedhydrocarbon, as used throughout the specification and claims, refers toany aliphatic or alicyclic hydrocarbon or mixture of hydrocarbons havinga higher hydrogen to carbon ratio than that of the cracked products.Preferably, primarily for economic reasons, the hydrocarbon feed formaking mixtures of acetylene and ethylene will consist essentially ofone or more of the lower aliphatic saturated hydrocarbons having atleast two to about ten carbon atoms per molecule, namely; ethane,propane, butane, isobutane, pentane, hexanes, octanes, nonanes, decanes.Commercial hydrocarbon mixtures derived from petroleum, such as naphtha,liquified petroleum gases or refinery byproduct gases are alsoapplicable. The process is also applicable to methane, but, in general,to obtain attractive yields of acetylene and ethylene by the process ofthis invention it is highly desirable that the feed contain substantialproportions of hydrocarbons higher than methane, especially hydrocarbonsin the range of C to about C Of course, heavier feeds may be used,especially if different products are desired.

The carbonaceous fuel may be any finely divided, e.g. about mesh orsmaller, combustible, solid, particulate, essentially carbonaceousmaterial, eg characterized by a hydrogen content of less than about 15percent, which is or has been treated to render it substantially freeflowing. Thus, for example, ground hard coal, devolatilized coal andchar obtained by low temperature carbonization of coal may be used. Itis a feature of the invention that carbonaceous fuels of widely varyingash contents may be employed with economic advantage, but superiorperformance is obtained when operating with coal having a high ashmelting point, e.g. greater than about 3000" F. Such coals are readilyavailable. In addition to the carbonaceous solid fuel mentioned above,supplementary fuel gas may be employed in relatively minor amounts, e.g.in sufficient amounts to supply not more than about 20 percent of thetotal heating value of the carbonaceous fuel and fuel gas combined. Thesupplementary fuel gas may be introduced separate from or in admixturewith the carbonaceous solid fuel. It would not involve a de parture fromthe spirit of the invention to employ supplementary liquid fuel;however, it will be appreciated that supplementary gaseous fuels aremore conveniently handled. Supplementary fuel gas can play an importantrole in helping to maintain combustion during the warm up phases ofreactor operation. However, once steady temperature conditions have beenattained, the supplementary fuel gas may be backed out and the reactormay be operated substantially exclusively on carbonaceous fuel, e.g.except for a very small gas-fueled pilot light to assist in ignition,only carbonaceous fuel is burned in the reactor.

Any oxygen bearing gas that will readily support combustion may beuseful as the oxidant in the process of the invention. In thisconnection, air has been employed with success. However, it will beappreciated that certain benefits, including a higher concentration ofthe desired products in the product stream, may be attained when oxygenis present in a higher concentration than is provided by atmosphericair. Thus, oxygen enriched air, oxygen and other gases may also beemployed as oxidant.

For quenching, it is possible to use any suitable fluid that is notdeleterious to the products or to the internals of the reactor andcollection system. Water is frequently employed. Also, refratcoryhydrocarbon oils may be used. Gaseous fluids, especially gaseoushydrocarbons, including feedstock or recycled cooled products of thecracking reaction, may also be employed.

The operating data for the process include various considerationspertaining to the container or chamber in which the reaction takesplace, the type and rate of flow of the materials, the temperature andpressure employed, the manner of quenching, and the residence time.

The interior of the container or reaction chamber will generally be inthe form of a cylinder, usually elongated. In this specification andclaims the term cylinder is used in a broad sense requiring neither acircular cross section nor strictly straight or parallel sidewalls. Thereaction chamber should be lined with any high temperature resistantrefractory material which is well adapted to withstand erosion due tohigh gas velocities and friction of solid particles combined withtemperatures in the range of 2700 F. and higher. Such refractories areavailable commercially, and high alumina castable refractory materialshave been found most suitable. The cracking chamber and the introducingmeans for the fuel and oxidant are preferably so dimensioned anddisposed that the fuel and oxidant travel through the cracking chamberclosely adjacent to at least one refractory sidewall thereof.

The feedstock, solid fuel and oxidant streams flow concurrently (in thesame general direction). The application of the term stream to the fuelsolids may seem inappropriate, since this term is most frequently usedto describe a flow of liquids or gases. Nevertheless, it serves a usefulfunction in this dosclosure, indicating that the solids move over agiven flow path in a substantially uniform concentration ordistribution.

The feedstock, fuel and oxidant streams may be completely separate fromone another at their points of introduction. However, it should beunderstood that a limited degree of mixing of said streams prior toreaching the cracking zone may be possible and in some cases desirable.For instance, some of the oxidant may be mixed with fuel solids beforeintroduction into the cracking chamber, so long as the major part of thecombustion takes place in said chamber, e.g. part of the oxidant may beused as a gaseous conveying/disbursing medium for the fuel. Whenoperating with heavy feedstocks, a small portion of the oxidant may beused as an atomizing medium for the feedstock. It should be understoodhowever that only a relatively small portion of the total oxidantemployed in the process is used for atomizing feedstock, and everyattempt is made to minimize diffusion between the main stream of oxidantand the hydrocarbon feedstock stream. Thus, substantially all of theoxidant (excluding amounts used to assist in the introduction of feedand fuel to the cracking zone) is introduced to and conducted throughthe cracking zone in such a manner as to maintain it substantiallyseparate from the feed stream until the streams have been diverted intoseparate recovery zones, or quenched or otherwise cooled or treated topreclude reaction between them.

The manner of introduction of the fuel Solids is preferably such thatthey are introduced as a stream intervening between the feedstock streamand the oxidant stream(s). The fuel solids have, in addition to theirlongitudinal velocity component, a velocity component perpendicular tothe cracking chamber axis and towards the oxidant stream(s). The objectof providing the perpendicular velocity component is to graduallydiffuse the solid particles into the oxidant stream(s). This results ina gradual burning of the fuel solids which continues from one end of thecracking zone to the other. The perpendicular velocity component will berelatively small in comparison to the longitudinal velocity component ofthe fuel solids, but should be sufiiciently large to incorporatesubstantially all of the fuel solids into the oxidant stream(s) beforereaching the end of the cracking zone.

When the flowing stream of feedstock and resultant products and thesubstantially separate stream of burning solid fuel, moving side byside, reach that portion of the cracking chamber where quenching is totake place, the necessity for maintaining separate streams ends,although as will be explained hereinafter, certain valuable economic andtechnical advantages will accrue from maintaining the separate identityof these streams during and after quenching. Thus, although it ispossible to quench both the cracked products and combustion gasestogether in a manner which promotes thorough turbulent mixing of thequench fluid with both the cracked products and the combustion gases,thus destroying the separate identity of said streams, the crackedproducts are preferably withdrawn from the reaction chamber separatefrom the combustion gases and are thereafter promptly quenched. Suchpractice facilitates economic recovery of the products and increases thethermal efficiency which may be obtained when using the combustion gasesin heat exchangers, boilers and the like as a heating medium.

The types of How which best promote the retention of the feedstock andoxidant in separate streams as above described may be readily attained.In the case of the feedstock, a linear flow is desired. The flow ofoxidant should be somewhat turbulent, but not sufiiciently turbulent tofully destroy its character as a stream or encourage diffusion into thefeed along the axis of the cracking chamber. Persons skilled in the artare aware of how to create a flow of gases characterized by linearity orany desired degree of turbulence by adjustment of gas velocity andsmoothness of flow path.

Those skilled in the art will readily appreciate that the charging ratesfor feedstock and oxidant may vary widely depending upon the dimensionsof the cracking chamber. The dimensions of the cracking chamber may bevaried widely without detriment to the process. However, for a crackingchamber of given dimensions, and given the residence time, temperaturesand pressures to be maintained within the process, one skilled in theart can readily compute the proper charging rates for oxidant, feedstockand solid fuel. The residence time for the feedstock should be in therange of 0.1 to 0.0001 second. The temperature and pressure conditionswithin the cracking zone will be discussed hereinafter.

Although, as explained above, it is not feasible to state limitingabsolute values for the charging rates for the materials introduced intothe reaction zones, certain generalizations can be made in regard to therelative volumetric charging rates for these materials. The fuel andoxidant should be introduced in a ratio which produces a stable flame.For any given reactor the proper ratio may readily be determinedempirically. The reactor disclosed herein has been operated withacceptable flame stability while introducing fuel and oxidant in aboutstoichiometric proportions and while introducing the air at 80 percentto 150 percent of the rate theoretically required to produce astoichiometric mixture of oxygen and fuel. In order to determine theproper charging rate for the hydrocarbon feedstock, one may calculatethe heat release of the fueloxidant mixture which is employed and then,by known thermal chemistry and thermodynamics, estimate the amount ofcracking stock that may be pyrolysised with a given quantity of fuel andoxidant. But in any case, optimum proportions of the fuel, oxidant andcracking stock can be established empirically.

Certain valuable benefits may be realized by controlling the relativevelocities of the feedstock stream and the burning stream ofcarbonaceous fuel and oxidant. By holding the velocities of said streamsas nearly equal as possible, interfacial slippage and turbulence betweenthe streams is thereby minimized to the fullest extent possible, and thediffusion of feedstock into the oxygen stream, with consequent loss bycombustion, it is thereby discouraged. Thus, where minimum loss offeedstock through interfacial mixing is highly critical it may be founddesirable to control the velocities of flow of the burning stream and ofthe feedstock stream to maintain them about equal, e.g. no more thanabout 20 percent difference. In this connection, it should be understoodthat adjustments can be made in the relative velocities of the streamswithout changing the relative volume flow rates of combustion gases andfeedstock by varying the cross-sectional areas of the streams. Thus, onecan attain the desired equality of veloctiy between the burning streamand the feedstock without destroying the quantitative and thermalbalance between the amount of feedstock on the one hand and the amountsof fuel and oxidant on the other.

For the purpose of discussing the temperatures which should be employedin the process of the invention, it may be useful to define certainzones: external oxidant preheat zone; external feedstock preheat zone;internal feedstock preheat zone; cracking zone; and quenching zone. Theexternal preheat zones are chambers outside the cracking chamber, inwhich zones preheating takes place. They may be heat exchangers,furnaces or the like in which the feedstock and oxidant are separatelyheated before introduction into the cracking chamber.

Preheating of the oxidant stream is highly desirable and, where theconcentration in the oxidant stream is low, may even be essential. Whenneeded, the external oxidant preheat zone is provided for this purpose.Air preheat temperatures ranging from about 200 to about 2000 F. areapplicable, and a temperature of about 500 1500 F. has been found quitesatisfactory in actual practice.

Because of the endothermic character of the process, certain definiteadvantages may be realized by preheating the feedstock to the maximumtemperature it can withstand without undue decomposition and consequentfouling of the preheaters. Thus, the feedstock should preferably beheated to a temperature slightly below the temperature of incipientcracking. The external feedstock preheat zone is provided for thispurpose. 'For many feedstocks a suitable maximum will be a temperaturein the range of about 1000 F. to about 1500 F.

The internal feedstock preheat zone is that portion of the upstream endof the cracking chamber in which the externally preheated feedstockstream is heated still further to the cracking temperature. Thehydrocarbon feedstocks to which the present invention is applicable maybe cracked to acetylene and mixtures of acetylene and ethylene byheating said feedstocks in the internal feedstock preheat zonetemperatures in the range of about 1500 to 3500 F., with temperatures inthe range of about 2000 to about 3200 F. being preferred. Thus, uponintroduction into the cracking chamber, the temperature of the feedstockshould be raised as rapidly as possible until within the aforesaidrange(s).

The cracking zone is that portion of the cracking chamber in which thefeedstock is at cracking temperature. The temperature of the feedstockis measured in or near the center of the feedstock stream, preferablynear the upstream end of the cracking zone. Temperatures somewhat higherthan those of the feedstock may be found in the surrounding burningstream, so care should be taken to see that it is the temperature of thefeedstock and not of the flame that is measured.

The maintenance of stable temperature in the feedstock stream in thecracking zone is extremely important in obtaining the kind oftime/temperature history which leads to the highest yields and the bestthermal efficiency. In accordance with the invention, the rate of heatrelease from combustion of the carbonaceous fuel is adjusted to besubstantially the same as the rate of heat consumption from cracking ofthe hydrocarbon stock and from normal losses, so that energy exchangevia radiation and any other applicable heat transfer mechanism(s)between and the cracking feedstock stream tends to maintain both streamsat the desired temperature. On at least three counts, carbonaceous fuelshave advantages which render them superior to hydrocarbon gases andvapors for this purpose.

First of all, the finely divided carbonaceous fuels offer great latitudeof control over combustion rate. Unlike gaseous hydrocarbons,carbonaceous solids can easily be ground to varying particle sizes, andthe combustion rates of carbonaceous solids are significantly affectedby changes in particle size. Thus, through a combination of adjustmentsin the particle size of the carbonaceous fuel, the oxidant preheattemperature and the fuel-oxidant mixing intensity, the combustion rateof the fuel may be varied widely, permitting easier matching of thecombustion rate to the cracking rate than is possible with gaseous andvaporous hydrocarbon fuels.

Secondly, in order that the above-described match between combustion andcracking rates may extend substantially throughout the cracking zone, aflame that is both long and steady is required. The cracking chamber maybe of significantly greater length than diameter and, if the flame is tocontinue to radiate heat to the feedstock throughout the length of thecracking chamber, the flame will have to extend throughout the length ofthe chamber. When it is attempted to produce a long flame withhydrocarbon gases and vapors, it will be found that a steady flame isexceedingly difficult if not completely impossible to attain, at leastunder the conditions that prevail in a cracking chamber. By a steadyflame is meant one which, to a very high degree, maintains substantiallyuniform length and is substantially free from wavering from side toside. The flickering, unstable flames that are obtained when it isattempted to produce a lengthy flame in a hydrocarbon cracking chamberby burning hydrocarbon gases and/or vapors reduce the thermal efliciencyof the cracking step and lower the yield by intermittently intrudingupon the feedstock stream. Surprisingly, however, it has been foundpossible to produce long flames of an exceptionally stable character ina cracking zone, using carbonaceous solid fuels, thus improving boththermal efficiency and yield.

Thirdly, the emissivity of the flames of solid carbonaceous fuels ishigher than the emissivity of the flames of hydrocarbon gases. Theincandescent hot burnning particles of carbonaceous solid fuel radiateheat into the feedstock stream at a faster rate than a stream ofhydrocarbon gas of the same B.t.u. content. As has been explained above,it is important that the heating of the feedstock to its crackingtemperature in the internal preheat zone takes place as rapidly aspossible, and the high emissivity of the flame of the solid carbonaceousfuel tends to produce more rapid heating than the flame of a hydrocarbongas or vapor fuel.

Where the solid carbonaceous fuel has a substantial ash content, as istrue of most coals, a definite advantage accrues from proportioning therates of introduction of feedstock, oxidant and solid carbonaceous fuelin such a way as to maintain temperature conditions below the ash fusiontemperature of the solid fuel and solid combustion products insubstantially every portion of the preheating and cracking zones throughwhich they may pass. If temperature conditions above the ash fusiontemperature are maintained, then any object within said zones which mayhave a lower temperature than the ash fusion temperature will tend toacquire a coating of coalesced ash which increases in thickness until anacceptable equilibrium thickness is reached or the flow of materialthrough the reactor is impeded by ash deposits to the point that thereis a volutary or involuntary shut-down for ash removal, or steps aretaken to continuously or periodically remove the ash during furnaceoperation. If it is desired to operate above the ash fusion temperaturefor and reason, the accumulation of an equilibrium thickness of ash maybe quite acceptable provided the sizes of the parts which will tend toaccumulate ash are chosen in such a manner that adequate space is leftfor process materials other than ash to flow through or past them, whenthe equilibrium thickness of ash is in place. Periodic shutdowns are tobe avoided, if possible, due to the lengthy procedures involved incooling off refractory-lined reactors and bringing them to reactiontemperature again. Reactors with means for continuously removing ashdeposits may be used in operations above the ash fusion temperature ifdesired. However, the simplest alternative from the standpoint ofminimizing the complexity of the operation and the reactor is to operatebelow the ash fusion temperature, and such mode of operation ispreferred. When this temperature limitation is observed, there will beno substantial tendency for ash to coalesce on the walls or quenchingmeans in quenching zone or On the eductor to be described hereinafter,and therefore no necessity of removing the resultant deposits therefrom.

The quenching zone is that portion of the cracking chamber or otheradjacent chamber in which the resultant cracked products are cooleduntil well below cracking temperature. The cooling should be carried outas rapidly as possible. Generally, the products should be quenched to atemperature of 800 F. or less. More preferably, the quench fluidtemperature, flow rate and mixing intensity should be controlled tolower the temperature of the products and/or combustion gases to atemperature not greater than about 500 F.

The process may be conducted at super-atmospheric pressure, atmosphericpressure and sub-atmospheric pressure. Operation at atmospheric pressurehas the advantage of convenience. However, under certain conditions,higher yields may be obtained by operating at a pressure of less thanone atmosphere.

Persons skilled in the art are thoroughly aware of the residence times(time intervals during which a feedstock and resulting products aresubjected to cracking temperatures) required to convert varioushydrocarbons to preselected products, including those hydrocarbons andproducts disclosed herein. Generally speaking, a residence time in therange of about to about 10- seconds is appropriate. Under certaincircumstances, e.g. when low residence times are employed, it may befound diflicult to have the feedstock and burning stream move at aboutthe same linear velocity and at the same time completely burn the solidfuel within the cracking zone. It would not therefore be contrary to thespirit of the invention to conduct part of the combustion of the solidfuel outside the cracking zone, before the fuel stream is brought intoproximity with the feedstock stream and/or after cracking has beencompleted and the products have been separated from the fuel. Thus,although it is preferred that the solid fuel be burned substantially tocompletion in the presence of the foodstock, such preference does notrule out the possibility of igniting and partly burning the solid fuelout of the presence of the feedstock. Beneficial results can be attainedwhen at least the major portion of the solid fuel is burned in thepresence of the feedstock. If a portion of the fuel is burned afterpassing through the cracking zone and after being separated from theproducts, such burning may be facilitated by injection of additionaloxidant into the combustion product stream. It is apparent, however,that the simplest procedure is to conduct substantially all of theburning of the solid fuel in the presence of the feedstock and themaximum benefits from radiant heat energy exchange between the burningstream and the feedstock are thereby obtained, thus making this thepreferred mode of operation.

The preferred products of the process will be acetylene, ethylene andvarious combustion product gases. Generally speaking, it is notconsidered economical under present conditions to attempt to produceacetylene and no ethylene or vice versa. However, by varying thefeedstock to fuel ratio, or the temperature in the cracking zone, or theresidence time or a combination of these and/ or other processconditions, the ratio of acetylene to ethylene in the products may bevaried. The acetylene/ethylene ratio which is chosen will depend uponcomplex economi variables and especially on the use to which the productstream will be put and the techniques used for separating the acetyleneand ethylene from the combustion gases.

The acetylene and/or ethylene may be separated from the cracking chambereffluent and, if desired, may be purified by any combination of knowntechniques, of which there are many. However, it is preferred thatsubstantially all of the acetylene and ethylene be withdrawn from thecracking chamber in a stream which contains less than half of thecombustion product gases and that the remainder of the combustion gasesdepart the cracking chamber as a separate stream. The acetylene-ethylenestream is then treated in accordance with any known technique toseparate the unsaturated products from the combustion products. A widevariety of separation techniques are contemplated, including, but notlimited to adsorption, selective chemical reaction, high pressuredistillation, solvent extraction and so forth.

DESCRIPTION OF A PREFERRED EMBODIMENT A preferred embodiment of theapparatus aspects of the invention will now be described with the aid ofthe accompanying drawings. In the preferred embodiment shown in FIGS. 2through 7, there is disclosed a solids feeding apparatus (FIGS. 2-4), athermal cracking apparatus (FIGS. 5A, 5B, and 6) and a recovery system(FIG. 7).

The provision of a solids feeding apparatus capable of delivering ahighly uniform flow of solids to the burner assembly is highly essentialto the attainment of a stable flame in the cracking chamber.Difficulties in attaining this objective in small experimental systemsmay possibly have been a deterrent to the development of solids-fueledcracking reactors in the past, since the solids-feeding problems thatwere experienced in the initial stages of making the present inventionwere substantial. The problems of feeding solids uniformly arecompounded in small systems because the ratio of solid particlesdimensions to feeder dimensions decreases as a given feeder is scaleddown. Erratic and cyclic fluctuations in solids delivery rates result inexperimental data which is quite different than that which would beobtained under highly stable conditions. The low residence timesassociated with the object of this invention make the problem of uniformsolids feeding particularly important. Heat transfer from an annularcombustion region to a central cracking region is dependent on flameluminosity or emissivity which is in turn dependent on the concentrationof carbonaceous solids in the primary air stream. Cyclic solids flow,solids agglomerate formation in the feeding and conveying system, anddead or stagnant zones in the conveying system which erraticallyaccumulate and discharge solids all result in pronounced deteriorationin system performance. The system which was developed to feed the solidsin the desired manner is presented as a disclosure in this patentapplication because, so far as the inventor knows, no suitableexperimental apparatus of this type was available heretofore, andconsequently achievement of the results included herein in small systemsappears to be contingent on the availability of the disclosed apparatusor one capable of equivalent performance.

The experimental solids feeding apparatus disclosed herein may besupported in any convenient manner (FIG. 2), but it is preferred to hangit from an overhead support 20 through a system of supporting membersincluding a weight measuring device 21, such as a strain gauge. As iswell known to those skilled in the art, such gauges are capable ofconverting a load or strain into an electrical signal representative ofthe weight suspended therefrom, which electrical signal may be conductedto a remote indicating panel or control device for monitoring orcontrolling the delivery rate of carbonaceous fuel. Mounted on hopper 22is an electric motor 23 provided with a reduction gear and thrustbearing assembly 24. The latter is connected by suitable coupling meansto a shaft 25 upon which are mounted an agitator 26 in the lower portionof the hopper and a feed screw 27 in an outlet tube 28 connected to thebottom of the hopper. The reduction gear 24 is preferably provided witha variable speed drive to permit control over the rate of rotation ofthe feed screw and thus over the solids delivery rate. Pulverized coalsuitable for boiler firing (60% by weight will pass 200 mesh), which isamong the various fuels useable in this system, has an angle of reposeof 90, thus necessitating precautions to insure that the feed screw 27runs full. The agitator 26 tends to maintain the bulk density of thesolids constant and independent of solids inventory. This in turnresults in a solids rate H which is independent of the amount containedin the hopper. The agitator also serves to prevent bridging andresultant fluctuations in the solids rate.

It will be noted that the feed screw is divided into two sections, anupper section of generally frusto-conical configuration which is thepickup section; and a lower or conveyor section which is of uniformflight diameter throughout its length. Although those skilled in the artwill readily recognize that these dimensions can be widely varied andthat there is no intention to be bound thereby, the following dimensionsand properties have been found desirable in such screw. The preferredconveyor section comprises a 1/1 pitch to diameter screw, 1 /2 inches indiameter and 12 inches long, with a 0.79 compression ratio (ratio ofintake channel depth to discharge channel epth), and a flight clearancevarying from 0.005 inch at the inlet to 0.007 inch at the discharge.Both the screw and the barrel 28 are machined from Ry-Alloy (trademarkof the Ryerson Company for their hardenable tool steel product) andsubsequenly heat treated to a 62-64 Rockwell C hardness. The screw rootsurface is polished to mirror like surface. This screw is designed tofeed 40 pounds per hour at -100 revolutions per minute. Theprogressively decreasing depth of the discharge channel of the feedscrew results in compression of the coal in the screw as it proceedsfrom the top of tube 28 to bottom, so that when the fuel reaches thedischarge end of the screw, the fuel is packed quite closely between theflights of the screw. This tends to prevent air leakage from thedischarge to the pickup of the screw and corresponding fluctuations insolids feed rate.

Outlet 28 is connected with a solids ejector nozzle assembly 29including an upper body portion 30 having a tapered bore or nozzle 31 offrusto-conical (60 angle) configuration therein. The conical nozzle ismounted directly below and in communication with feed screw 27, and hasa longitudinal axis coinciding with that of the tube 28, and has aninternal diameter at its upper end corresponding to the internaldiameter of the latter. The nozzle tapers down to an outlet 32 ofapproximately /3 the foregoing diameter, at which point it opens into aconduit section 33. A plurality of passages 34, provided with supplyconduits 35, are interspersed about the conical surface, intersectingtangentially therewith and at a 45 angle to its longitudinal axis. Thepurpose of the passages 34 is ot conduct air or other gas in a swirlingdownward movement to prevent carbonaceous fuel solids from bridgingacross the conical walls. The supply pipes 35 are connected with anysuitable source of pressurized flowing gas, e.g. air, for this purpose.In a solids ejection nozzle in which the nozzle tapers from 1.5 inchinlet to a 0.5 inch outlet and in which there are three tangentiallydisposed passages 34 spaced at equal intervals about the periphery ofthe cone, an air flow of one-hundred s.c.f.h. has been found suitable.

The longitudinal axis of the conduit section 33, directly below theconical nozzle, is perpendicular to the axis of the latter. There is anopening in the conduit section 33 in registry with the outlet 32 of theconical section to permit fuel solids to enter same. A coaxial conduit36 of smaller diameter than conduit 33 is positioned in the latter, andterminates in an open end adjacent the projected end of conical section31, but does not block the outlet thereof. The conduit 36 is supportedin place by the closed end 37 of conduit 33. In a solids ejection nozzlehaving the dimensions previously stated, and in which the conduitsection 33 has a inch inside diameter and the air supply conduit 36 hasa inch outside diameter, an air flow of approximately 600 s.c.f.h. hasbeeen found suitable for creating a reduced pressure (as compared tothat in the hopper 22) in the conical section and assisting in thewithdrawing of the coal solids therefrom. The provision of a conduit 46connecting conduit 33 and hopper 22 has also been found helpful in thatit tends to reduce or eliminate the pressure differential across screw27.

The portions of the solids feeding system described thus far are for thepurpose of establishing a controlled rate of flow of fuel solids in aconduit, such as conduit 33. However, in the process of setting up acontrolled rate of flow of coal solids with a screw, agglomeration mayoccur, to a varying extent. Therefore, the solids feeding apparatus isprovided with means for breaking up any such agglomerates that mightform and for attenuating small fluctuations in the flow of solids comingfrom the feed screw. As will be apparent from FIG. 4, the conduit 33extends to the inlet of a hammer mill type grinder 38. It will be notedthat the largest part of the length of conduit 33 is disposed as avertical run into the top of the grinder. The grinder, which may becooled by a water jacket if desired, breaks up any agglomerates formedin the compression section of the screw 27 and discharges the groundfuel suspension through a screen (not shown) with one-sixteenth diameterround holes into a conduit 39 which extends to the fuel entry inlet 60of the cracking reactor 40.

The system just described has been found adequate for feeding fuelsolids over extended periods at acceptably stable rates appropriate foroperation of the reactor disclosed herein. Since the ratio of solidparticle dimensions to feeder dimensions will increase as the feedingsystem is scaled up, it appears that the problems of building anoperable production scale unit would be no greater, and would probablyin fact be smaller. The throughput of a production-sized solids feedingsystem might well reach 100 tons per day or higher. Grinding, meteringand conveying equipment for such through-puts is readily available. Acontemplated production sized unit could include a Fuller-Kinyon pumpfeeding /a x 0 dry coal (less than 5% moisture) to a ball mill, rod milor other grinding device capable of producing a pulverized boiler fuel.The grinder would discharge a continuous flow of solids and conveyingair to the cracking reactor.

Other supporting apparatus for the reactor include supply and meteringapparatus for the feedstock and supply and metering apparatus for theoxidant. Such equipment is quite familiar to persons skilled in thecracking art and it will not therefore be described in detail. However,examples of such equipment are illustrated schematically in FIG. 4. Asshown therein, a supply of feedstock is connected through pneumaticcontrol valve 81 to recording flow controller 82 which controls valve 81through a feedback control loop 83 to maintain a constant flow offeedstock into feedstock inlet tube 50 of the reactor 40. The controller82 is of a type which has an adjustable set point, permittingpreselective variable control over the feedstock flow rate any any givenoperating temperature. When the oxidant is air, a conduit 84 may be usedto withdraw air directly from the atmosphere into a rotary centrifugalair pump 85 which discharges into a pneumatic flow control valve 86 andinto a branch conduit 36 which feeds conveying air through a regulatingvalve 87 to solids ejector nozzle 29, including conduits 35. Suchconveying air travels with the dispersed fuel solids through conduit 33,grinder 38 and conduit 39 and enters the reactor 40 through fuel solidsinlet 60. Such air is sometimes referred to herein as primary air. Theair which proceeds from blower 85 through valve 86 is sometimes referredto herein as secondary air. The valve 86, flow controller 88 andfeedback loop 89 constitute a preselective variable control means forthe flow of the primary oxidant stream which, after passing thecontroller, enters the reactor through inlet tube 71. Preheaters foroxidant and feedstock are conventionally used in conjunction withcracking reactors, and they (not shown) may be included in the foregoingsystem at any convenient location.

The reactor 40 shown in FIGS. A and 5B includes the followingsub-portions: cracking chamber 42 and its side wall means 43; burner 41;product educator tube 44, including quenching means; and combustionproduct collection chamber 47 with off-gas and ash handling means.

The side wall means 43 of cracking chamber 42 is a cast tube ofrefractory material such as Harbison Walker Castolast G high aluminarefractory cement. The tube is cast and cured in accordance withconventional procedures commonly employed by those skilled in the art offabricating high temperature resistant refractory linings for crackingreactors, such as those used in the carbon black art. The tube employedin this preferred embodiment is of precisely circular cross section, hasa uniform diameter and is straight throughout its length, and has thefollowing dimensions: ID. 3''; 0D. 12''. The inner surface of the wallmeans is free from turbulence-inducing projections and roughnessthroughout the length of the zone in which cracking is intended to takeplace. Thus, no sharp changes of direction, chokes, checkerwork, orother obstructions are included within that portion of the crackingchamber where cracking is to take place.

To the upstream end of the cracking chamber is secured a burner 41. Thelatter includes a base plate 55 which is connected to the refractorytube perpendicular to its longitudinal axis at the upstream end thereof.The plate 55 supports the inlet means for feedstock, oxidant and fueland forms a closure or upstream end wall for the cracking chamber. Thesurface of plate 55 which faces chamber 42 is also referred to herein asthe burner face. Although it is not required to be so, the burner faceis planar in this embodiment, and the apertures through which the fuel,feedstock and oxidant gain admission to the cracking chamber are in theburner face, so that they are all located in the same plane. For thepurpose of supporting certain parts of the introducing means for thefeedstock and fuel, a conduit member 56 is secured to the plate 55 onthe extended longitudinal axis of chamber 42. The conduit 56 has aninner end of reduced cross section which fits into an opening of reducedcross section in the outer surface of plate 55, into which the conduitis fixedly secured. An opening of the same diameter as the inside ofconduit 56 is cut through the burner face so as to be disposed inregistry with the inside of the conduit. Disposed coaxially within theconduit 56 is a conduit 50 which terminates at the burner face, but islonger than conduit 56. Conduit 50 is a straight run of tubing ofuniformly circular cross section having a length to diameter ratio onthe order of about to 1 which ratio may if desired be decreased slightlyto less than 20 to 1 or increased to infinity. In the presentembodiment, the conduit is Ms inch in inside diameter and 20 incheslong.

In the present preferred embodiment, the source 80, valve 81, controller82 and control loop 83, which were mentioned previously, as well as theconduit 50, considered collectively, constitute the feedstockintroduction means, with the conduit 50 constituting the nozzle whichdirects the feedstock stream into the cracking chamber. The innersurface of the walls of conduit 50 constitute a streamforming memberwhich as a consequence of its position,

shape and dimensions, carries out the function of confining the flow ofhydrocarbons (eg. feedstock and/or products) or at least the majorportion thereof, to a flow path which occupies less than about half ofthe transverse cross-sectional area of the cracking chamber. Bytransverse crosssectional area is meant the area of the chamber measuredin a plane perpendicular to the longitudinal axis of the chamber. Therequirement for confining the hydrocarbons to this limited cross sectionextends throughout that portion of the chamber in which the hydrocarbonsare travelling in unobstructed side-by-side relationship with theburning fuel (no intervening barrier) and are at combustion inducingtemperatures. However, once the hydrocarbons have entered a zone inwhich they are separated from the oxidant by a physical barrier and/ orhave been cooled to temperatures at which combustion is no longer asubstantial danger, the confining requirement no longer exists. Anyother feedstock stream forming member which performs or assists in thefunction of confining the flow of the major portion of the feedstock tothe specified cross section at least until it reaches the downstream endof the cracking zone may be added to or substituted for the conduit 50,even if the confining effect thereof is less than perfect or evensomewhat crude. Thus, for instance, feedstock nozzles with drag-inducingmembers therein on their longitudinal axes for slowing the velocity ofthe center of the stream, or feedstock nozzles with other than circularcross section may be used. It is preferred, however, to use that type ofnozzle which promotes the least possible mixing of the feedstock withthe burning fuel and the unobstructed, 20 to 1 or greater length todiameter ratio, circular cross section tube is considered best for thispurpose at the present time.

The conduit 50 is provided with a cooling jacket 51 having an interior54 and coolant inlet 52 and outlet 53. The outer surface of the coolingjacket 51 and the inner surface of the conduit 56, respectively, definethe inner and outer boundaries of an annular fuel introductionpassageway 59 closed off at one end by an apertured cap 57 and gas-tightgasket 58 and the coolant circulating in interior 54 of cooling jacket51 helps prevent sticking of the fuel particles on passageway 59. Thedownstream end of passageway 59 constitutes a port which opens throughthe burner face into cracking chamber 42 surrounding conduit 50. Theterm surrounding, wherever used in the present specification and claims,means that the item described thereby, e.g. said part, encircles morethan half of the way around the feedstock nozzle conduit 50. Theaforesaid part preferably extends substantially all the way around theconduit 50 in the burner face, so that the feedstock stream will beenclosed substantially completely by the fuel stream. Thus, an annularopening is desirable. However, this does not rule out the provision ofbraces or spokes in the annular fuel opening for main taining alignmentbetween the conduits 50 and 56, so long as such braces or spokes aredimensioned, shaped and finished in such a manner that they do notunduly disturb the desired flow of fuel solids. Thus, braces in the formof fixed turbine blades extending between the conduits may be used toadvantage both for maintaining alignment between them and for impartinga rotational com.- ponent of motion to the fuel stream. It has beenfound however that the same result can be obtained at a lower cost ofconstruction by wrapping the exterior of the cooling jacket 51 with thewires 61 whose diameters are substantially the same as the spacingbetween the jacket and conduit 50, the turns of wire being separatedlongitudinally to provide one or more helical passages. Thus, in thispreferred embodiment in which the conduit 50 is 1" x 16 gauge x 347 ss,the cooling jacket 51 is 1.25" x 16 gauge x 347 ss and the conduit 56 isa 1.5" conduit, 12 /8" diameter wires 61 are silver soldered to theexterior surface of the cooling jacket 51 so that they are angularlyspaced from one another in the annular passageway 59 at about 30intervals and rotate through about the periphery of conduit whiletraversing a longitudinal distance of about 3" in said passageway. Thisassembly, and the blower 85, valve 87, conduit 36, solids feederassembly of FIGS. 3 and 4, conduit 33, grinder 38, conduit 39 andtangential entry fuel inlet into passageway 59, considered collectively,consitute a preferred means for introducing solid carbonaceous fuel intothe cracking chamber 42 with components of motion downstream in saidchamber and divergent from the general direction of movement of thefeedstock stream.

In this embodiment the centrifugal force generated by rotation of thefuel stream is the factor which induces its outward component of motionwhich causes its direction of movement to diverge from that of thefeedstock. However, rotation-inducing fuel introducing means are notrequired. For instance, the wires 61 may be omitted and the open end ofpassageway 59 may be flared as it approaches the burner face. Varioustypes of deflectors may be used without departing from the scope of theinvention.

Spaced outwardly from passageway 59 in the walls of conduit 56 are apair of passages 62 and 63 which have been provided to conduct a mixtureof oxygen or air and fuel gas from an external source, not shown, to anannular distribution chamber whence such mixture is directed throughtwelve pilot lights 66 equally spaced (angularly) from one anotheraround the longitudinal axis of conduit and having their dischargeoutlets between the fuel introduction port and the oxidant introductionmeans to produce pilot flames 68.

Surrounding the passageway 59, and preferaby spaced outwardly from thepilot lights 66 is an oxidant introduction means 69 extending throughthe plate and the burner face and communicating between the interior ofmanifold 70 and that of the chamber 42. The walls of manifold 70 aresecured in gas-tight relationship to the top of plate 55 and theperiphery of the conduit 56. The oxidant supply conduit 71 enters themanifold tangentially through inlet 72. The oxidant introduction means69 may take various forms. For instance, it may be an annular port, orit may be a number of (e.g., twelve) passageways arranged at equally,angularly spaced intervals about the longitudinal axis of conduit 50.The oxidant introduction means should be adapted for distributing theoxidant as evenly as possible around the periphery of the chamber 42.The data set forth in the example hereinafter was obtained with areactor in which the oxidant introducing means is twelve passageways asabove described. However, there is some evidence that even betterperformance can be obtained with an annular port.

Regardless of its form, it is considered advantageous for the feedstockintroducing means to be spaced outwardly from the feedstock conduit 50by a substantial distance, e.g. a distance which is at least equal tothe radius of the conduit 50. The feedstock introducing means can bedirected either in the same direction as the feedstock conduit 50 or ina divergent direction but should not be directed in a convergentdirection. Such divergence is particularly useful in embodiments of theinvention in which the chamber 42 has divergent walls and thehydrocarbon stream is permitted to freely expand as it moves downstream.However, in the present embodiment, the passageways 69 are arranged withtheir longitudinal axes parallel to that of feedstock conduit 50 andchamber 42, so that they direct at least the major portion of theoxidant (e.g. secondary air) downstream in the chamber 42 adjacent sidewall means 43. Such a mode of construction is simple and appearssatisfactory. It should be understood that the oxidant inlet need not bein the form of a single annular port or single circle of spacedpassageways. A plurality of such circles or ports or one or more of eachin combination with the other may be provided. In any event, suchannular port(s) or passageway(s), or other kinds of outlet or outletstaken together with the blower 85, valve 86, control loop 87, controller88, conduit 71, and manifold 70, constitute an acceptable oxidantintroducing means for producing an envelope of oxidant surrounding thefuel and for directing the oxidant downstream while keeping it spacedoutwardly from at least the major portion of the feedstock stream.

As previously indicated, the use of a planar burner face in which theopenings through which the feedstock, fuel and oxidant all gain accessto cracking chamber 42 are all in the same transverse plane is a matterof convenience in construction and is by no means essential. If desired,one or more of the inlets for the fuel, feedstock and oxidant may beplaced an appreciable distance downstream in the chamber. 'For example,a frusto-conical burner face may be employed in which the long radiusend of the frusto-conical burner is situated at the upstream end of thecracking chamber, the short radius end of the burner extends downstreamin the chamber, and the axis of the burner coincides with that of thechamber. In such case, the feedstock opening may be in the smallcircular downstream end of the frusto-conical burner member on thelongitudinal axis thereof, and the fuel and oxidant inlets may beannular ports located at longitudinally spaced points in the conicalsurface. Such a construction is particularly useful in a reactor inwhich the walls of the cracking chamber diverge towards the downstreamend thereof. In this connection, it should be understood therefore, thatthe use of the term surrounding to express the spatial relationshipbetween the fuel inlet and the feedstock inlet on the one hand, and theoxidant inlet and the fuel inlet on the other, does not require thatthese inlets be in the same plane. Rather the term is used, aspreviously mentioned, to convey the idea that one inlet encircles theother, and if the requisite degree of encirclement can be seen in atransverse crosssection of the reactor looking upstream from a pointimmediately downstream of the inlets in question, then the requirementof surrounding has been met. For similar reasons, the terms outward andoutwardly should not be interpreted as requiring that the things oractions designated thereby exist or take place in the same transverseplane. It should be apparent therefore that the details of constructiongiven herein in respect to the preferred embodiment are illustrativeonly and many variations thereon, falling within the spirit of theinvention, will occur to those skilled in the art.

In order to protect the plate 55 from the high temperatures generatedwithin the cracking chamber 42 by the combustion of the solid fuel andoxidant, it has been found desirable to provide the plate with cooling.This has been done by providing a circular groove 73 in the uppersurface of plate 55, and by covering over said groove with a circularcover plate 74 to form a leak-proof passage. Cooling fluid, e.g. wateris admitted to said passage by a supply pipe 75 and departs throughoutlet pipe 76.

While any conventional quenching, product withdrawal and recovery systemmay be used with the portions of the reactor discussed thus far, weprefer to use the eductor tube shown in FIGS. 5A and 5B and the recoverysystem shown in FIG. 7. In the preferred embodiment disclosed herein,the eductor tube 44 is stationed on the longitudinal axis of crackingchamber 42 with its inlet port directed towards feedstock conduit 50. Inreactors of differing configuration, it might be necessary to locate theeductor in reference to some point other than the cracking chamber axisin order to intercept the highest concentration of cracked products, butwith the reactor shown herein the axial location is preferred. Theeductor may be supported in any convenient manner either fixed ormoveable, and may be attached to any convenient part of the reactor.However, in the reactor shown herein, it is preferred that the eductorbe supported in the bottom wall of the combustion product collectionchamber 47,

The chamber 47 comprises top wall 95, side walls 96, and bottom wall 97in which is disposed at stufiing box 98 centered about the extended axisof chamber 42 and in registry with passages 104 and 103 formed in theupper and lower walls, respectively, of chamber 47. Pas sage 103 is ofslightly larger diameter than the outside of eductor tube, while passage104 is of slightly larger diameter than the inside of the crackingchamber. The eductor tube extends from outside the chamber 47, throughstuffing box 98, through passage 103, through chamber 47 and throughpassage 104 into cracking chamber 42. The stuffing box includes packing99 and a packing nut 100 for compressing the packing against the sidesof eductor tube 44 and against the outer end of passage 103. With thenut loosened, the eductor tube may be extended or retracted axially toplace its port 105 at any desired distance from the end of feedstockconduit 50. The nut 100 may then be tightened to immobilize the eductortube in the desired position.

Because of the very high temperatures required in the cracking chamber,and the fact that the eductor will ordinarily be made of steel insteadof refractory material, some sort of internal cooling is usuallyrequired. This may be accomplished by building the tube of inner 101 andouter 102 concentric conduits forming an annular coolant passage 106within the body of the eductor. The passageway 106 should transverse atleast that portion of the length of the eductor which is extendible intothe cracking chamber 42, and preferably transverses, as shown in FIGS. Aand 5B, so much of the tube as is extendible into the reactor, includingnot only chamber 42, but chamber 47 as well. The coolant passage ispreferably closed off at both its inner 107 and outer 108 ends, and theinner tube 101 extends beyond the outer end of said passage forconnection with any suitable product recovery system, such as that shownin FIG. 7. Coolant, such as a gas or liquid, e.g. water, may gain entryto coolant passage 106 through a fresh coolant delivery conduit 109communicating with said passage from outside the reactor.

In accordance with the invention, the eductor may be provided with anyconvenient form of used coolant outlet at any convenient location.However, it is preferred that the used coolant outlet should be situatedin a portion of the eductor which is within the reactor, where it may beused for quenching the cracked products. In its most preferred form thecoolant outlet means comprises a plurality of outlets 110 communicatingbetween coolant passageway 106 and the interior of conduit 101 adjacentinlet port 105. Thus disposed, the waste coolant outlets may be used todirect coolant into the cracked products as they enter the eductorthrough port 105, thus quenching them. Without any intention of beingbound thereby, the following dimensions are set forth as constitutingpreferred dimensions for the eductor: outer tube 102, 1.50" x 16 gauge x347 ss; inner tube 101, 125" x 16 gauge x 347 ss; and waste coolantoutlets 110, 24 in number, .02" in diameter, equally spaced in groups of8 about 3 circles, Ms and respectively from the inner end 107 of theeductor. Those skilled in the art will recognize that these dimensionsmay be readily varied to suit various reactors and operating conditions.

Because the outer transverse dimensions (e.g. diameter) of the eductorassembly are substantially less than the transverse dimensions (e.g.diameter) of the inside of the cracking chamber, an annular passageway45 of appreciable width is provided therebetween. This passageway isprovided for hot products of combustion to depart the reactor and may beprovided with an injector to burn any coal which reaches this pointwithout having burned. It should be apparent that the eductor tube maybe used in cracking reactors in which other than solid carbonaceous fuelis used. However, in the present embodiment, the passageway 45 willconduct both gaseous and solid (ash) products of combustion. Passageway45 communicates through passageway 104, with chamber 47, where thegaseous combustion products may be drawn off 24 through outlet 111 andany solids which collect therein can be periodically removed through ascuttle 112.

As shown in FIG. 7, the conduit 101, through which the quenched crackedproducts depart the eductor and the reactor, is connected to a quenchfluid separator 123 having a fluid outlet 124 and a cracked productsoutlet conduit 125. Conduit 125 communicates with a gas/solids separatorsystem 126 (e.g. agglomerator and bag filter) which is used wheneversolid cracked products (e.g. carbon black) are being produced. Thegas/solids separator system outlet 127 discharges into a conduit 128.When no solids are being produced, the gas/solids separation system maybe by-passed and the quench-fluid-free prod ucts may be passed directlyto conduit 128 by opening by-pass valve 129. A pneumatically-actuatedmotor valve 130 and differential pressure transmitter/controller 131 arelocated in conduit 128, the controller 131 being interconnected with themotor in valve 130 through a feedback loop 132. Between the controllerand valve is a vacuum gauge 133 for visual reading of the vacuum inconduit 128. On the downstream side of the controller 131, conduit 128connects to the suction side 122 of a steam ejector 120, an aspiratortype device which uses steam from a supply conduit 121 to pull a vacuumon the conduit and on the eductor upstream through the quench waterseparator 123, gas/solids separator 126 or by-pass valve 129, motorvalve 130 and controller 131. Steam and gaseous cracked products departthe ejector through outlet 134 into condenser 119 which converts thesteam vapors to entrained liquid. The entrained liquid and crackedproducts depart condenser 119 into condensate separator 118 whichdelivers condensate through a condensate outlet 117 and substantiallyliquid free cracked gaseous products through a product outlet 116.Outlet 116 may be connected to any suitable product purification orrecovery device of which a wide variety are known to persons skilled inthe art. Accordingly, no description of such devices will be givenherein.

The differential pressure controller/transmitter is of a type having apreselective variable setpoint, so that it can open and close motorvalve 130 to maintain any selected vacuum in conduit 128, and in conduit101. Since the pressure in cracking chamber 42 is also con trolled, bycontrolling the rates of flow of feedstock, fuel and oxidant and therate of combustion, the ejector 120, controller 131, control loop 132,and valve 130, considered collectively, constitute an acceptable meansfor producing a controlled negative pressure dilferential between theinteriors of the cracking chamber and eductor.

The use of the eductor tube and associated means for producing theaforesaid pressure differential contribute certain operatingefficiencies to the cracking processes. For instance, the products arediluted to a much lesser extent with combustion gases than in the caseof the usual precombustion, partial combustion and other pyrolyticcracking processes. This reduces the size and cost of the recoverysystem needed to handle the cracked products. It also considerablyreduces the extent of purification needed to put the product in asaleable or usable form. The use of the eductor avoids the necessity ofquenching all of the hot combustion gases in the reactor to cool theproducts, so the heating value available from the waste combustion gasesis available for recovery at a high level of thermal efficiency insteadof being wasted. The movable feature of the eductor tube facilitatesprocess control, in that it makes possible quick adjustment of theresidence time of the feed and products without the necessity ofaltering the rates of introduction of fuel, oxidant and feedstock intothe reactor. It has been found possible to extend and retract theeductor tube over substantial distances within the cracking chamberwithout adversely affecting reactor operation.

25 EXAMPLE This examples illustrates the operation of the process andapparatus described above:

Process conditions Feed: Propane Propane temperature: 1100 F. Propanerate: 63.5 pounds per hour Fuel: #2 Gas Seam Coal from Boone County, W.Va.,

supplied by Obelbay Norton B.t.u. content (moist. & ash free basis): perpound 14,500 Ash content: 7% H content: 7% Volatile content: 33% Ashfusion temp.: 2800" F.+ S content: 0.8% Fixed C: 60% PS1: 5 Percentpassing 325 mesh sieve: 60% Moisture content: 2% Fuel rate: 31 poundsper hour Oxidant: Air Air temperature: 1100 F. Air rate: 5800 s.c.f.h.

Percent air introduced as secondary air: 90% (appi-ox.) Percent of airintroduced as primary air for suspending coal: 10% (approX.) Distance ofeductor from burner face: 4.5 inches Quench fluid: Water Watertemperature at inlet to eductor: 80 F. Water rate: 3.5 g.p.h. Pressurein reactor: 1 lb. p.s.i.g. Refractory temperature: 3000 F. Residencetime of hydrocarbons in cracking chamber: 1

millisecond (approx) Quenched products temperature: 150 F. Flow rate ofquenched products stream: 850 s.c.f.h.

The flame exhibits good stability and has an intense orange to whitecolor. No supplementary fuel gas is used after start-up, except for thenegligible amount of fuel gas consumed by the pilot lights. The gas fromthe eductor and from the annular passage surrounding it are sampledunder steady state conditions and are analyzed. The results of theanalysis are set forth as follows:

Volume (percent) In annu- In eduelar pas- Component tor sage Out As C H10.4 AS C2H4 As C s 0.1 As CH 3.0 As CO 7.9 As CO 18.8 As carbon black14.0

Total 58.6

Unaccounted for (Unburned carbon in coal) 16.9

In conclusion, while the foregoing specification and drawings describethe construction, operation and use of certain preferred embodiments ofthe instant invention, it is to be understood that there is no intentionto limit the invention to the precise constructions and arrangementsherein disclosed, since the various details of construction, form andarrangement may obviously 'be varied to a considerable extent by anyperson skilled in the art without really departing from the basicprinciples and novel teachings of this invention and Without sacrificingany of the advantages thereof. Accordingly, the appended claims areintended to encompass all changes, variations, modifications andequivalents falling within the scope of the invention.

What is claimed is:

1. A hydrocarbon cracking process comprising supplying a hydrocarbonfeed stock stream, a flow of finely divided, particulate, solid,combustible carbonaceous fuel and oxidant to a confined cracking zone,said fuel being introduced into said zone as at least one stream whichis separate from the major portion of the oxidant and which intervenesbetween said oxidant and said feed stock stream; burning said flow insaid zone; conducting said hydrocarbon feed stock stream through saidcracking zone adjacent to and concurrently with but substantiallyseparate from said burning flow of oxidant and carbonaceous fuel;retaining said feed stock stream in the presence of but substantiallyseparate from said burning flow for a time and at a temperaturesufficient to crack said feed stock; and recovering the resultantcracked products.

2. The process of claim I conducted in the substantial absence of steam.

3. The process of claim 1 conducted in the substantial absence ofhydrocarbon fuel.

4. An improved cracking process comprising flowing a hydrocarbon feedstock downstream in a cracking zone and cracking said feed stock thereinby subjecting it to heat transferred thereto by combustion of aconcurrently flowing stream of solid, particulate carbonaceous fuel withan oxidant, said fuel being introduced into said cracking zone inintervening relationship between said feed stock and the major portionof the oxidant, and thereafter Withdrawing first and second separatestreams from said cracking zone, the first of said streams having ahigher concentration of cracked products than said second stream.

5. The process of claim 1 wherein said feedstock stream and the burningflow of solid carbonaceous fuel flow through said zone as generallyconcentric streams.

6. Process according to claim 5 wherein said feedstock stream issurrounded by said burning flow.

7. Process according to claim 5 wherein said feedstock, said fuel andthe major portion of the oxidant are each introduced into said zoneseparately from the other, moving in the same general direction, withsaid feed stream being surrounded by the fuel and said fuel beingsurrounded by the major portion of said oxidant.

8. Process according to claim 7 wherein a minor portion of the oxidantis mixed with said carbonaceous solid fuel as a suspending medium priorto their introduction into said zone.

9. Process according to claim 7 wherein said fuel stream is introducedwith a component of motion downstream in said zone and with a componentof motion away from said feedstock and toward the major portion of theoxidant.

10. Process according to claim 9 wherein said fuel stream is rotated toprovide said component of motion away from said feedstock.

11. Process according to claim 1 wherein the rate of combustion of saidcarbonaceous solid fuel is controlled by adjustment of the particle sizethereof.

12. Process according to claim 1 wherein the rate of combustion of saidcarbonaceous solid fuel is controlled for sustaining the combustion ofsaid particles substantially throughout the length of the cracking zoneand for completing the combustion of said particles substantially at thedownstream end of said cracking zone, whereby the hot, high emissivity,incandescent, burning carbonaceous fuel particles radiate heat into thefeedstock substantially throughout the entire length of the crackingzone, thus continually adding heat to the reaction mass by radiant heattransfer to make up for heat abstracted therefrom by the endothermiccracking reaction.

13. Process according to claim 1 wherein a stream rich in the resultantcracked products is isolated within said cracking zone from the majorportion of the resultant combustion products and is removed from saidchamber as a separate stream.

14. Process in accordance with claim 1 wherein said hydrocarbonfeedstock is a fluidic feedstock selected from the group consisting ofaliphatic and alicyclic hydrocarbons.

15. Process according to claim 1 wherein said feed stock is fed in agaseous state.

16. Process according to claim 1 wherein said hydrocarbon feedstockincludes a major weight proportion of aliphatic saturatedhydrocarbon(s).

17. Process according to claim 16 wherein said hydrocarbon(s) have anaverage of at least two carbon atoms per molecule.

18. Process according to claim 1 wherein said carbonaceous fuel has amaximum particle size of substantially sixty mesh.

19. Process according to claim 1 wherein said carbonaceous fuel ischaracterized by a hydrogen content of less than about percent.

20. Process according to claim 1 wherein said carbonaceous fuel is amember selected from the group consisting of ground coal, devolatilizedcoal, coal char obtained from low temperature carbonization of coal, andmixtures thereof.

21. Process according to claim 1 wherein said solid carbonaceous fuel ischaracterized by an ash fusion point of at least about 3000 F.

22. Process according to claim 1 wherein at least about 80% of the heatgenerated in said cracking zone is generated by the combustion of saidsolid carbonaceous fuel.

23. Process according to claim 1 wherein said oxidant is a free-oxygencontaining gas.

24. Process according to claim 23 wherein said gas is air.

25. Process according to claim 1 wherein said feedstock is a fluidichydrocarbon feedstock containing from about 2 to 10 carbon atoms permolecule, said feedstock being retained in said cracking zone at atemperature of about 1500 F. to about 3500 F. for a residence time inthe range of about 10 to about 10 seconds for converting saidhydrocarbon feedstock to a product mixture comprising acetylene andethylene.

26. Process in accordance with claim 25 wherein said temperature is inthe range of about 2000 F. to about 3200 F.

27. Process in accordance with claim 1 wherein the rate of heat releasefrom combustion of said carbonaceous fuel is maintained substantiallyequal to the rate of heat consumption from cracking of said hydrocarbonfeedstock and from normal losses for maintaining said streams atsubstantially stable temperatures by energy exchange therebetween duringtheir passage through said zone.

28. Process according to claim 1 wherein said solid carbonaceous fuel isburned in the form of a long, stable flame extending substantiallythroughout the length of the cracking zone.

29. Process in accordance with claim 13 wherein the temperature of thecracked products in said isolated stream is rapidly reduced to atemperature of not more than 800 F. at the downstream end of thecracking zone.

30. Process in accordance with claim 29 wherein the temperature of the.cracked products in said isolated stream is rapidly reduced to not morethan about 500 F. in the quenching operation.

31. Process of claim 1 conducted at atmospheric pressure.

32. Process according to claim 1 wherein heat is transferred from saidburning flow to said feedstock in said zone for cracking said feedstockwithout any structural member intervening therebetween and, subsequentto the cracking of said feedstock, the resultant cracked products areisolated from said combustion products by a structural barrier andquenched out of the presence of said combustion products.

33. An improved cracking process comprising the combined steps of:continuously feeding a gaseous hydrocarbon cracking stock, a finelydivided, combustible, particulate solid carbonaceous fuel, and a gaseousoxidant into and through a confined cracking zone; in said zone, burningsaid carbonaceous fuel substantially separate from but in sufiicientlynear proximity to said hydrocarbon feedstock, to provide the heatnecessary for cracking said feedstock in said cracking zone to crackedproducts; said feedstock being fed into said cracking zone in the formof at least one stream separate from said carbonaceous fuel and oxidant;said solid fuel and the major portion of said oxidant being maintainedseparate from one another until entering said cracking zone and being ignited therein; said carbonaceous fuel being introduced in asubstantially intervening relationship between said feedstock and saidmajor portion of said oxidant for discouraging combustion of saidfeedstock; controlling the rate of combustion of said carbonaceous solidfuel products for sustaining the combustion of said particlessubstantially throughout the length of said cracking zone, whereby thehot, high emissivity, incandescent, burning carbonaceous fuel particlesradiate heat into said feedstock substantially throughout the entire.length of said cracking zone, thus continually adding heat to saidfeedstock to make up for heat abstracted by the endothermic crackingreaction and normal heat losses.

34. Process according to claim 33 wherein said process is conducted withsaid carbonaceous fuel being used substantially exclusively as the heatgenerating medium for said cracking reaction.

35. Process according to claim 33 wherein said process is conducted inthe substantial absence of water vapor, including steam.

36. Process in accordance with claim 33 wherein said cracked productsand said combustion products are isolated from one another prior toquenching of the cracked products.

37. A cracking process comprising introducing a flow of oxidant into acracking chamber establishing a quantity-controlled flow of combustiblesolid particulate carbonaceous fuel, scattering said flow of fuel in astream of gaseous suspending medium, sending the resultant solidcarbonaceous fuel suspension to said cracking chamber, introducing saidsuspension into said cracking chamber in the form of at least one streamconcentric with an inner stream of hydrocarbon feedstock moving in thesame general direction, said solid carbonaceous fuel suspensionintervening between said feedstock and at least 29 30 the major portionof the oxidant and having a compo- 2,498,444 2/1950 Orr 260683 nent ofmotion in the same general direction as said feed- 2,707,148 4/ 1955Kollgaard 208126 stock and another component of motion away from said2,767,233 10/1956 Mullen 260683 feedstock, igniting said solid fuelsuspension in said crack- 2,790,838 4/1957 Schrader 260683 ing chamber,cracking said feedstock through the action of the heat provided bycombustion of said solid carbonaceous fuel; and recovering the crackedproducts sep- PAUL COUGHLAN, JR, Primary Examiner arate from saidcombustion products.

C. E. SPRESSER, JR., Assistant Examiner 5 2,805,131 9/1957 McIntire260679 References Cited 10 UNITED STATES PATENTS US. Cl. X.R.

1,892,559 12/1932 Hillhouse 260679 260679; 208126 2,413,407 12/1946Dreyfus 260-683

